1. Field of Invention
This invention is directed to determining the design parameters for lines screens.
2. Description of Related Art
Most marking technologies, such as offset printing, laser printing, and inkjet printing, use halftone printing techniques to form a pictorial region on an image receiving substrate based on continuous tone input image data. That is, such conventional image forming techniques represent continuous tone or gray scale image data using halftone techniques that integrate between portions of the image that are completely printed at a full density and portions of the image that are left unprinted, such that the background color is visible. When this is done at a high enough spatial frequency, the human visual system perceives this combination of full color and background color to be a gray scale value between the background color and the full color.
In “An Optimum Algorithm for Halftone Generation for Displays and Hard Copies”, by T. Holladay, Proceedings of the SID, Vol. 12, no. 2, 1980, which is incorporated herein by reference in its entirety, Holladay discloses a method for creating a halftone cell that forms a screen pattern at some desired angle to the process/scanning directions. The screen pattern is formed by repeatedly tiling the halftone cell over the plane of the image receiving substrate. The resulting screen pattern includes rows of dots, each dot made from a number of pixels. Holladay's technique allows for the halftone screen to be created at various desired angles. Conventionally, digital cluster dot screens use isometric dots, i.e., dots having the same length side vectors ā and b. Moreover, conventionally, digital cluster dot screens are normally square, such that the vectors ā and b are at right angles to each other. Because of the geometric constraints, the angles and frequencies that can be achieved using Holladay's technique are significantly limited.